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CY8CKIT-025 PSoC® Precision Analog Temperature Sensor Expansion Board Kit Guide, Doc. # 001-65791 Rev. *J 7
1. Introduction
Thank you for your interest in PSoC solutions for temperature sensing. The CY8CKIT-025 PSoC
®
Precision Analog Temperature Sensor Expansion Board Kit (EBK) together with the example
projects provide complete solutions demonstrating PSoC-based temperature sensing. The
CY8CKIT-025 board connects with the CY8CKIT-030 PSoC 3 Development Kit (DVK), CY8CKIT-
050 PSoC 5LP Development Kit, or the CY8CKIT-001 PSoC Development Kit. The kit supports
temperature measurement using four temperature sensors:
■
Thermocouple
■
Thermistor
■
Resistive Temperature Detector (RTD)
■
Diode
Note
: The TempSense example project outputs one more temperature value read from the DS600
IC. This is used for cold junction compensation for the thermocouple and not intended as an option
for the onboard temperature sensor.
The four sensors have their own advantages and limitations. The choice of a sensor for an
application depends on the cost, accuracy required, and temperature measurement range.
Thermocouples measure temperatures in a wide range, from –250
°
C to 2300
°
C. However, the
voltage change is not linear and takes more CPU cycles for temperature computation.
Thermocouples require another temperature sensor, such as the thermistor, diode, or RTD, to
measure the cold junction temperature. The DS600 IC or the thermistor can be used for cold junction
compensation of the thermocouple. A thermistor, diode, or RTD cannot measure temperatures
greater than 850
°
C. Thermocouples have a very good response time.
Thermistors have a highly nonlinear curve and take more CPU cycles for temperature computation.
They measure temperature in the range –100
°
C to 200
°
C. Thermistors have a good response time
and they are less expensive when compared to RTDs and thermocouples.
RTDs have a linear and repeatable resistance variation with temperature, making it easier to
compute temperature accurately. They measure temperature from –200
°
C to 850
°
C. RTDs are
expensive due to their linearity and accuracy. RTDs have a lower response time compared to a
thermistor or thermocouple.
Diodes are the cheapest sensors for temperature measurement. They measure temperature in the
range –50
°
C to 150
°
C. Accurate temperature measurement is difficult with a diode. Table 1-1
shows a comparison among the four sensors.